Effects of Ergotamine Tartrate on Prolactin and Growth Hormone Secretion by Rat Adenohypophysis in vitro1

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Abstract
The effects of ergotamine tartrate (ET) on prolactin secretion by rat adenohypophysis in vitro were investigated to ascertain the site of inhibitory action of the drug on the secretion of this hormone. Prolactin levels in incubation medium were estimated by disc electrophoresis and densitometry. Intraperitoneal injection of 1 mg ET 4 hr or 15 hr prior to incubation of the adenohypophyses of the recipient female rats resulted in significant inhibition of prolactin release in vitro. The drug was more effective after 4 hr than after 15 hr. Addition of ET to incubation medium at concentrations ranging from 2.5 to 20 µg/ml resulted in significant inhibition of prolactin release in a 4-hr incubation experiment. A dose-related effect was obtained over a narrow range of ET concentrations. Concentrations of the drug ranging from 0.005 to 5.0 µg/ml significantly inhibited prolactin secretion in two organ culture experiments of 24-hr duration with male rat adenohypophyses. In the first experiment about 40% inhibition of prolactin secretion was obtained at all concentrations of ET. In the second organ culture study, all concentrations of the drug inhibited secretion by more than 95%. Thus, no dose-related effect was obtained in either organ culture experiment. None of the concentrations of ET significantly affected growth hormone secretion in organ culture. The solvent of the ET containing tartaric acid had no effect on prolactin secretion in a 24-hr organ culture experiment. Neither the ET nor its solvent containing tartaric acid had any effect on the detectability of prolactin in the disc electrophoretic-densitometric assay system. The results indicate that ergot drugs inhibit prolactin-dependent reproductive processes by depressing the secretion of the hormone by acting directly on the adenohypophyseal lactotropes.

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